Baby sleeping bag tog guide: what to use and when

The NHS safer sleep page gives the general ranges below for commercial baby sleeping bags.

These are room temperatures, not the overnight forecast. A heated bedroom can need a lighter bag in December than an unheated room does in April.

The table doesn't prescribe a vest-and-sleepsuit combination. The Lullaby Trust explains why it cannot provide one clothing and tog chart for every baby: materials, the warmth trapped between layers and individual babies all differ.

Start with the clothing combination in that bag's instructions for your measured room temperature. There isn't one outfit that works under every 2.5 tog bag.

Lay out the clothes next to the bag before bedtime. Check whether the guide specifies a short-sleeved vest, a long-sleeved vest, a sleepsuit or a combination. A vest under a sleepsuit is an extra layer; it's easy to overlook it when you're counting.

If you've lost the guide, look up the exact model on the manufacturer's website. A chart for another bag from the same brand may cover different materials or a different design.

Then check your baby. Feel their chest or the back of their neck. If they're hot or sweaty, remove a layer. Cool hands and feet alone don't tell you they need more clothes.

20°C falls at the join between the NHS ranges. That doesn't mean the two bags are interchangeable with the same clothes underneath.

Check the temperature range and clothing instructions for each bag you own. If both include 20°C, follow the combination for the one you choose, then check your baby's chest or neck. Don't put a lighter bag over a heavier one or add a blanket to bridge the difference.

Read the 20°C guide for overlapping tog ranges and warm bedrooms.

The season alone doesn't tell you. Check the room and the instructions for the bag. The NHS general table above doesn't include a 3.5 tog range, so don't invent one by extending the numbers.

If the room is below 16°C, try to bring it into the recommended 16–20°C range where you can. If your baby's chest feels cold, the Lullaby Trust advises an extra clothing layer or a higher tog bag. Follow the product guidance, and don't add blankets over a sleeping bag.

If keeping the room warm is difficult, ask your health visitor for advice about your circumstances. You don't need to solve it by piling more bedding into the cot.

Check the minimum weight and size requirements. The neck and arm openings should fit so your baby cannot slip down inside. Buying a larger size to grow into can defeat that fit.

• Use one sleeping bag, without additional bedding over it.
• Keep hats and hoods off for indoor sleep.
• Avoid weighted sleeping bags and weighted bedding.
• Put your baby on their back in a clear cot with a firm, flat mattress. For the first six months, keep their sleep space in the same room as you.

You can have the right number on the label and still need to adjust the clothes. The useful habit is checking your baby, rather than treating the chart as a guarantee.